Two-stage desulfurization with solvent deasphalting between stages

ABSTRACT

AN ASPHALTIC, HYDROCARBONACEOUS CHARGE STOCK, CONTAINING MORE THAN ABOUT 2.0% BY WEIGHT OF SULFUR, IS CONVERTED TO FUEL OIL IN A PLURALITY OF CATALYTIC CONVERSION ZONES. THE FIRST ZONE EFFLUENT IS SEPARATED TO PROVIDE AN ASPHALTENE CONCENTRATE WHICH IS SUBJECTED TO SOLVENT DEASPHALTING. THE REMAINDER OF THE FIRST ZONE EFFLUENT, IN ADMIXTURE WITH THE DEAPHALTED PRODUCT, IS FURTHER REACTED IN A SECOND CATALYTIC REACTION ZONE. THE FUEL OIL PRODUCT, IN ADMIXTURE WITH THE PRECIPITATED ASPHALTICS, HAS A SULFUR CONCENTRATION LESS THAN ABOUT 1.0% BY WEIGHT.

July 24, 1973 c. H. wATKlNs TWO-STAGE DESULFURIZATION WITH SOLVENT DEASPHALTING BETWEEN STAGES Filed Deo. 14, 1971 RSM STES S l mi n United States Patent O 3,748,261 TWO-STAGE DESULFURIZATION WITH SOLVENT DEASPHALTING BETWEEN STAGES Charles H. Watkins, Arlington Heights, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill. Filed Dec. 14, 1971, Ser. No. 207,871 Int. Cl. Cg 31/14 U.S. Cl. 208-210 7 Claims ABSTRACT OF THE DISCLOSURE APPLICABILITY OF INVENTION Desulfun'zation is a process well known and thoroughly described in petroleum technology, the literature relating thereto being replete with references directed toward suitable desnlfurization catalysts, methods and techniques of catalyst manufacture and various operating techniques utilized. Desulfurization connotes the destructive removal of sulfurous compounds, through the conversion thereof to hydrogen sulfide and hydrocarbons, and is often included in the broad term hydrorefining Hydrorefining processes are effected at operating conditions which serve to promote denitrification and desulfurization primarily, and asphaltene conversion, non-distillable hydrocarbon conversion, hydrogenation and hydrocracking to a somewhat lesser extent. In other Words, the terms hydrorefining and desulfurizaton are generally employed synonymously to allude to a process wherein a hydrocarbon fed stock is cleaned-up in order to prepare either a charge stock suitable for utilization in subsequent hydrocarbon conversion, or to recover a product having an immediate utility. The combination process of my invention can be beneficially utilized to produce a fuel oil containing less than about 1.0% by Weight of sulfur, while simultaneously effecting some conversion into lower-boiling hydrocarbon products.

Recent recognition of the necessity to inhibit the discharge of pollutants into the atmosphere has resulted in governmental limitations being imposed in a number of areas. Notable among these concerns the burning of highsulfur content fuels, principally coal and fuel oil, which results in atmospheric discharge of exceedingly large quantities of sulfur dioxide. With respect to fuel oils, derived from petroleum crude oils, the demand therefor has increased significantly as a result of increased energy requirements; of greater importance, however, is the fact that legislation has already been imposed in many locales limiting the concentration of sulfur to a maximum of 1.0% by weight or less. Experts in this particular area are currently predicting that the next several years will see the maximum sulfur content of fuel oils being restricted to a level less than about 0.5% by Weight. It is to this end that the present invention is specifically directed; that is, the production of hydrocarbonaceous fuel oils containing less than about 1.0% by weight of sulfur, and, where required, to a level less than about 0.5% by weight. The increasing demand for low sulfur fuel oils has also brought about the necessity for effecting the conversion of the bottom of the barrel. In other words, the

3,74,20l Patented `l'uly 24, 1973 ICC increasing demand for fuel oil has in turn necessitated this utilization of virtually 100.0% of a petroleum crude o1 In accordance with the present combination process, acceptable fuel oils are derived via the desulfurization of petroleum crude oils, atmospheric tower bottoms products, Vacuum tower bottoms products, heavy cycle stocks, crude oil residuum, topped crude oils, heavy hydrocarbonaceous oils extracted from tar sands, etc. Crude oils, and the heavier hydrocarbon fractions and/or distillates obtained therefrom, contain nitrogenous and sulfurous compounds in exceedingly large quantities, the latter generally being in the range of about 2.5% to about 6.0% by weight. In addition, these heavy hydrocarbon fractions, often referred to in the art as black oils, contain large quantities of organo-metallic contaminants, principally comprising nickel and vanadium, and high molecular weight insoluble asphaltenes. Illustrative of those charge stocks, to which the present invention is applicable, are a vacuum tower bottoms product having a gravity of 7.1 API and containing 4.05% by weight of sulfur and 23.7% by weight of asphaltenes; a topped Middle-East crude oil, having a gravity of 11.0 API, and containing 10.1% by Weight of asphaltenes and 5.20% by weight of sulfur; and, a vacuum residuum having a gravity of about 8.8 API and containing 3.0% by weight of sulfur, 4,300 p.p.m. by weight of nitrogen and having a 20.0% volumetric distillation temperature of about 1055 F. The utilization of the process of the present invention affords maximum recovery of low-sulfur content fuel oil from these heavier hydrocarbonaceous charge stocks.

OBJECTS AND EMBODIMENTS A principal object of the present invention is to provide a process for effecting the desulfurization of hydrocarbonaceous material. A corollary objective resides in a multiple-stage process for desulfurizing heavy hydrocarbonaceous material in order to produce an acceptable fuel oil containing less than about 1.0% by weight of sulfur.

Another object is to aord a desulfurization process for the maximum recovery of a fuel oil product from hydrocarbonaceous black oils.

In one embodiment, therefore, the present invention involves a process for producing fuel oil containing less than about 1.0% by weight of sulfur from an asphaltic hydrocarbonaceous charge stock containing more than about 2.0% by weight of sulfur, which process comprises the steps of (a) reacting said charge stock and hydrogen in a first catalytic reaction zone, at desulfurization conditions selected to convert sulfurous compounds into hydrogen sulfide and hydrocarbons; (b) separating the resulting first reaction zone efiiuent, at substantially the same pressure, in a first separation zone to provide a first vaporous phase and a first normally liquid phase; (c) deasphalting at least a portion of said first liquid phase with a selective solvent in a solvent extraction zone to provide a solvent-rich normally liquid phase and a solvent-lean asphaltene concentrate; (d) reacting at least a portion of said vaporous phase and said solvent-rich liquid phase with hydrogen, in a second catalytic reaction zone, at desulfurization conditions selected to convert additional sulfurous compounds into hydrogen sulfide and hydrocarbons; and, (e) separating the resulting second reaction zone eiuent, in a second separation zone, at substantially the same pressure and a temperature of from 60 F. to about F., to recover a fuel oil product containing less than about 1.0% by weight of sulfur.

Other embodiments of my invention, as hereinafter set forth in greater detail, reside primarily in preferred ranges of process variables, various processing techniques and preferred catalytic composites for utilization in the fixedbed catalytic reaction zones. For example, in one such other embodiment, the precipitated asphaltene concentrate is admixed with the :fuel oil product recovered from the second separation zone in order to increase the overall volumetric yield.

In another such embodiment, the operating conditions employed within the rst catalytic reaction zone are selected to reduce the sulfur concentration to a level below about 2.0%, and preferably within the range of about 1.25% to about 1.75% by weight.

Other contemplated objects and embodiments of my invention will become evident from the following, more detailed description of the combination process encompassed thereby.

SUMMARY OF INVENTION Before summarizing my invention, several definitions are believed necessary in order that a clear understanding thereof be afforded. IIn the present specication and appended claims, the phrase substantially the same as is intended to connote that the pressure under which a succeeding vessel is maintained, is the same as that in au upstream vessel, allowing only for the pressure drop experienced as a result of the flow of uids through the system. Similarly, the phrase temperature substantially the same as" is employed to indicate that the only reduction in temperature stems from the normally experienced loss d-ue to the liow of the material from one piece of equipment to another, or from conversion of sensible heat to latent heat by liashingf The present invention utilizes at least two xed bed catalytic reaction zones having separation facilities and a deasphalting zone therebetween. Although the catalytic composites will be of different physical and chemical characteristics in many instances, they may be identical. Regardless, the catalytic composites utilized in the present combination process comprise metallic components selected from the metals of Groups VI-B and VIII of the Periodic Table, and compounds thereof. Thus, in accordance with the Periodic Table of the Elements, E. H. Sargent & Co., 1964, suitable metallic components are those selected from the group consisting of chromium, molybdenum, tungsten, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum. Additionally, recent investigations have indicated that catalyst composites, for utilization with excessively high-sulfur content feed stocks, are improved through the incorporation of a zinc and/or bismuth component. While neither the precise composition, nor the method of manufacturing the various catalytic composites is considered essential to my invention, certain aspects are preferred. For example, since the charge stocks to the present process are extremely heavy, it is preferred that the components of the catalyst possess the propensity for effecting hydrocracking while simultaneously promoting the conversion of sulfurous compounds into hydrogen sulfide and hydrocarbons. The concentration of the catalytically active metallic component, or components, is primarily dependent upon the particular metal as well as the physical and/ or chemical characteristics of the charge stock. For example, the me tallic components of Group VI-B are generally present in an amount Within the range of about 4.0% to about 30.0% by weight, the `Iron-group metals in an amount Within the range of about 0.2% to about 10.0% by Weight, whereas the noble metals of Group VIII are preferably present in an amount within the range of about 0.1% to about 5.0% by Weight, all of which are calculated as if these components existed within the catalytic composite in the elemental state. In many instances, particularly when processing heavier hydrocarbonaceous charge stocks containing a significant quantity of hydrocarbons boiling above a temperature of about 950 F., the carrier material will comprise a crystalline aluminosilicate, or zeolitic molecular sieve. Such Zeoliti material includes mordenite, faujasite, Type A or Type U molecular sieves, etc. Although the zeolites may be employed in a substantially pure state, it is contemplated that they may be included within an amorphous matrix such as silica, alumina, and mixtures of alumina and silica. It is further contemplated that the catalytic composite may have a halogen component incorporated therein, such component selected from fluorine, chlorine, iodine, bromine and mixtures thereof. The halogen Will be composited with the carrier material in such a manner as results in a lfinal catalytic composite containing from about 0.1% to about 2.0% by weight of the halogen component, calculated as the element.

The metallic components may be incorporated within the catalytic composite in any suitable manner including co-precipitation, or co-gellation with the carrier material, ion-exchange, or impregnation of the carrier, either before, or after calcination. Following the incorporation of the metallic components, the carrier material is dried and subjected to a high temperature calcination or oxidation technique at a temperature of about 750 F. to about 1300 F. When a crystalline aluminosilicate is utilized within the carrier material, the upper limit for the calcination technique is preferably about 1000u F.

With respect to the operating conditions imposed upon the catalytic reaction zones, they are selected primarily to effect the conversion of sulfurous compounds into hydrogen sulde and hydrocarbons. In general, those imposed upon the second reaction zone will result in a greater operating severity. However, the suitable ranges 4for the various operating variables will be the same for both reaction systems. Thus, the pressures will range from about 500 to about 3,500 p.s.i.g., and preferably from 1,000 to about 2,500 p.s.i.g. The maximum catalyst bed temperature should not exceed 900 F., to a great extent, the lower limit preferably being 600 F. Since the reactions being etfected are principally exothermic, an increasing temperature gradient will be experienced as the reactants traverse the catalyst bed. Preferred operating techniques dictate that the increased temperature gradient be limited to a maximum of F. In order to control the temperature gradient, it is within the scope of the present invention to employ quench streams, either normally liquid, or normally gaseous, at one or more intermediate points of the catalyst bed. The hydrogen concentration is expressed as standard cubic feed per barrel of charge stock, and will generally be within the range of about 1,500 to about 30,000. Liquid hourly space velocities, delned as volumes of normally liquid hydrocarbons charged per hour, per volume of catalyst disposed within the given reaction zone, will be from 0.25 to about 2.50.

The eluent from the first reaction zone is introduced, at substantially the same pressure, into a hot separator at either substantially the same temperature, or` after cooling to a level not substantially below about 600 F. A principally vaporous phase is recovered, and serves as a portion of the feed to the second reaction zone. Although the liquid phase may be directly introduced into the deasphalting zone, a preferred technique utilizes a second separation zone, at substantially the same temperature, but at a significantly lower pressure below about 200 p.s.i.g., and preferably sub-atmospheric, in order to recover additional distillables and to further concentrate the asphaltenes. For this purpose, a standard vacuum column is most suitable. The additional distillables and the deasphalted oil are then introduced into the second reaction zone along with the vaporous phase from the hot separator.

The second zone elfluent is separated to provide a hydrogen-rich vaporous phase for recycle to the first reaction zone, preferably following hydrogen sulfide removal, and to recover a low-sulfur content fuel oil product. The separation is effected at substantially the same pressure and at a lower temperature within the range of 60 F. to about 140 F.

The present combination process utilizes a solvent deasphalting, or solvent extraction zone, to separate an unreacted asphaltic concentrate from at least a portion of the first reaction zone effluent. It must necessarily be acknowledged that the prior art is replete with a wide spectrum of techniques for effecting solvent deasphalting of asphaltene-containing hydrocarbonaceous charge stocks. It is understood that no attempt is herein made to claim solvent deasphalting other than as its use as an integral element of the combination process as herein described. Any suitable solvent deasphalting technique known in the prior art may be utilized, several examples of which are hereinafter described. In the interest of brevity, however, no attempt will be made to tabulate exhaustively the solvent deasphalting art.

Exemplary of such prior art is U.S. Pat. No. 1,948,296 (Class 208-4) in which a combination process is described wherein the separated asphaltic fraction is admixed with a suitable oil and subjected to oxidation to obtain a particularly good asphalt. The described solvents, for utilization in precipitating the asphaltic fraction, include light petroleum hydrocarbons such as naphtha, casinghead gasoline, light petroleum fractions composed of propane, n-butane and isobutane, certain alcohols, ether and mixtures thereof, etc.

U.S. Pat. No. 2,002,004 (Class 208-14) involves a twostage deasphalting process wherein the second stage completes the precipitation of asphalts which was partially effected in the first stage. As noted previously, the solvents described include naphtha, gasoline, casinghead gasoline and liquefied normally gaseous hydrocarbons such as ethane, propane, butane and mixtures thereof.

U.S. Pat. No. 2,914,457 (Class 208-79) describes a multiple combination process involving fractionation, vacuum distillation, solvent deasphalting, hydrogenation and catalytic reforming. Again, the suitable liquid deasphalting solvents include liqueed normally gaseous hydrocarbons such as propane, n-butane, isobutane and mixtures thereof, as well as ethane, ethylene, propylene, nbutylene, isobutylene, pentane, isopentane, and mixtures thereof.

In accordance with the present invention, the product eflluent from the initial reaction zone is separated to provide a heavy normally liquid phase concentrated in asphaltenes. At least a portion of this heavy liquid phase is introduced into an upper portion of a solvent deasphalting zone, wherein it countercurrently contacts a suitable selective solvent which is introduced into a lower portion thereof. The solvent deasphalting zone will function at a temperature in the range of about 50 F. to about 500 F., and preferably from about 100 F. to about 300 F.; the pressure will be maintained within the range of about 100 to about 1000 p.s.i.g., and preferably from about 200 to about 600 p.s.i.g. The precise operating conditions will generally depend upon the physical characteristics of the change stock as Well as the selected solvent. In general, the temperature and pressure are selected to maintain the deasphalting operation in liquid phase, and to insure that substantially all the asphaltenes are removed in the solvent-lean heavy phase.

Suitable solvents include those hereinbefore described with respect to prior art deasphalting techinques. Thus, it is contemplated that the solvent will be selected from the group of light hydrocarbons such as ethane, methane, propane, butane, isobutane, pentane, isopentane, neo-pentane, hexane, isohexane, heptane, the mono-olefiic counterparts thereof, etc. Furthermore, the solvent may 'be a normally liquid naphtha fraction containing hydrocarbons having from about 5 to about 14 carbon atoms per molecule, and preferably a naphtha fraction having an end boiling point below about 200 F. The solvent-rich normally liquid phase is introduced into a suitable solvent recovery system, the design and techniques of which are thoroughly described in the prior art. As hereinafter set forth, the solvent-lean heavy phase is preferably combined with the low sulfur fuel oil product in order to increase the overall volumetric yield.

DESCRIPTION OF DRAWING One embodiment of the present invention is presented in the accompanying drawing by means of a simplified ow diagram in which details such as pumps, instrumentation and controls, heat-exchange and heat-recovery circuits, valving, start-up lines and similar hardware have been omitted as not essential to an understanding of the techniques involved. The utilization of such miscellaneous appurtenances, to modify the illustrated process flow, is well within the purview of those skilled in the art of petroleum rening operations and techniques. With reference now to the drawing, the illustrated embodiment will be described in conjunction with a commerciallyscaled unit processing a 482 F .-plus fraction derived from Kuwait crude oil. The charge stock, having a gravity of 18.9 API, and containing 3.50% by weight of sulfur, is introduced into the process by way of line 1, being admixed with a hydrogen-rich recycle gaseous phase in line 2, and containing make-up hydrogen, to supplant that consumed in the overall process, being introduced through line 3. The charge stock feed rate is 68,354 bbl/day, the hydrogen concentration is about 5,000 s.c.f./bbl., and the mixture continues through line 2 into reaction zone 4. The intended object is to recover a maximum quantity of fuel oil having a sulfur content less than about 0.5% by weight.

The pressure imposed upon reaction zone 4 is about 2,000 p.s.i.g., and the liquid hoursly space velocity is 0.6. The catalyst bed inlet temperature is controlled to maintain the maximum reaction temperature at a level of about 700 F. Reaction zone 4 contains a catalytic composite of an alumina carrier material, about 5.0% by weight of nickel and about 11.0% by weight of molybdenum.

The total reaction product etliuent is withdrawn by way of line 5 and introduced therethrough into hot separator 6 at substantially the same pressure, and a temperature of about 800 F. The normally liquid phase, in an amount of 54,470 bbL/day is withdrawn from hot separator 6 by way of line 7, and introduced into vacuum column 8 at a temperature of about 795 F.; the vacuum column is functioning at about 25 mm. Hg, absolute, through the utilization of standard vacuum jets not illustrated in the drawing. Vacuum bottoms, in an lamount of about 17,040 bbl/day, is withdrawn through line 9 and introduced into deasphalting zone 10 wherein the same is countercurrently contacted with a solvent consisting of a mixture of n-butane and isobutane. An asphaltene-containing concentrate, in an amount of about 2,406 bbl/day, is removed from deasphalting zone 10 by way of line 11.

The principally vaporous phase withdrawn by hot separator 6, by way of line 12, is admixed with the vacuum gas oil (37,430 bbl/day) in line 13 and the deasphalted oil (14,634 bbl./day) in line 14, the mixture continuing through line 12 into reaction zone 15.

The catalyst disposed in reaction zone 15 is identical to that disposed within reaction zone 4. The pressure in reaction zone 15 is about 1900 p.s.i.g., the maximum catalyst bed temperature being controlled at a level of about 800 F., while the liquid hourly space velocity therethrough is about 1.20. The product eliluent is withdrawn through line 16, introduced into cold separator 17 wherein the same is separated to provide the hydrogenrich gaseous phase in line 2 and `a normally liquid product stream in line 18. Cold separator 2 serves as the focal point for pressure control within the system. Prior to being introduced into cold separator 17, the product elueut in line 16 is utilized as a heat-exchange medium, and further cooled to a temperature of about F.

As illustrated, in a preferred embodiment, the normally liquid phase in line 18 is admixed with the asphaltene concentrate in line 11, from which mixture the desired crude oil product is recovered in fraction-ation facilities not illustrated in the accompanying drawing. With respect to the original topped Kuwait crude oil, through the utilization of the present combination process, 66.987 bbL/day (98.0% by volume) of 400 F.-plus fuel oil, the sulfur concentration of which is 0.3% yby Weight, is recovered.

I claim as my invention:

1. A process for producing fuel oil containing less than `about 1.0% by weight of sulfur, from an asphaltic hydrocarbonaceous charge stock containing more than about 2.0% by weight of sulfur, which process comprises the steps of:

(a) reacting said charge stock and hydrogen, in a first catalytic reaction zone, at desulfurization conditions selected to convert sulfurous compounds into hydrogen sulde and hydrocarbons;

(b) separating the resulting rst reaction effluent, at substantially the same pressure, in a rst separation zone, to provide a tirst vaporous phase and a iirst normally liquid phase;

(c) deasphalting at least a -portion of said rst liquid phase with a selective solvent in a solvent extraction zone to provide a solventrich normally liquid phase and a solvent-lean asphaltene concentrate;

(d) reacting at least a portion of said first vaporous phase and said solventrich liquid phase with hydrogen, in a second catalytic reaction zone, at desulfurization conditions selected to convert additional sulfurous compounds into hydrogen sulfide and hydrocarbons; and

(e) separating the resulting second reaction zone eflluent, in a second separation zone, at substantially the same pressure and a temperature of from 60 F. to about 140 F., to recover a fuel oil product containing less than about 1.0% by weight of sulfur.

2. The process of claim 1 further characterized in that said solvent-lean asphaltene concentrate is admixed with said fuel oil product.

3. The process of claim 1 further characterized in that said tirst normally liquid phase is further separated at a substantial reduced pressure, in a third separation zone, to provide a second vaporous phase and a second normally liquid phase, and deasphalting said second liquid phase in said solvent extraction zone.

4. The process of claim 3 further characterized in that at least a portion of said second vaporous phase is reacted in said second reaction zone.

5. The process of claim 1 further characterized in that said desulfurization conditions include a pressure from 500 to about 3,500 p.s.i.g., a maximum catalyst bed temperature from about 600 F. to about 900 F., a hydrogen concentration in the range of about 1,500 to about 30,000 scf./bb1. and a liquid hourly space velocity of from 0.25 to about 2.50.

6. The process of claim 1 further characterized in that said .rst and second reaction zones have disposed therein a catalytic composite of Ia porous carrier material, a Group VI-B metal component and a Group VIII metal component.

7. The process of claim 1 further characterized in that a third vaporous phase is withdrawn from said second separation zone and recycled, at least in part, t0 said irst catalytic reaction zone.

References Cited UNITED STATES PATENTS 2,971,905 2/ 1961 Bieber et al. 208-252 2,973,313 2/ 1961 Pcvere et `al 208-86 3,095,368 6/1963 Bieber et al. 208-252 3,119,765 1/1964 Corneil et al 208-210 3,691,152 9/ 1972 Nelson et al. 208-210 DELBERT E. GANTZ, Primary 'Examiner S. L. BERGER, Assistant Examiner U.S. Cl. X.R. 208-58 

